Tubular reactors are ubiquitous in the manufacture of commodity chemicals, in particular in processes wherein continuous operation is desired or required. The ideal flow condition in a tubular reactor is ‘plug flow’, and under such ideal conditions, the residence time in the reactor is the same for all elements of fluid and there is typically a uniform velocity profile across the radius of the reactor. Product mixing is also ideally limited to material the same age, i.e. mixing occurs in the radial direction only. That is, as the plug flows through the reactor, the plug components are perfectly mixed in the radial direction, with mixing in the axial direction being nonexistent.
While in practice, ideal plug flow does not occur, maintaining reasonably good plug flow (such that the flow profile closely resembles plug flow velocity profile) through tubular reactors provides significant benefits. For one, plug flow provides greater separation between reacted and unreacted material than non plug flow. This is desirable for processes where reaction rate is affected by reactant concentration. And, good plug flow permits precise control of residence time, which can be critical in processes where conversion and/or selectivity are sensitive to the same.
Many factors can impact the ability to provide plug flow conditions approximating ideal. For example, substantial mixing in the axial direction can reduce the quality of plug flow, as can wall friction and diffusion, etc. The effects of many of these can be mitigated by increasing the fluid velocity and/or reactor channel length. Achieving the right combination of residence time, efficient mixing and good plug flow can result in tubular reactors that are hundreds of meters long. Reactors of such length can then present additional difficulties in temperature control and heat transfer characteristics.
It would thus be desirable to provide a tubular reactor capable of approximating plug flow, while yet also providing optimal, e.g., residence time, heat transfer characteristics, temperature control and mixing.